The present invention relates to an image recording material in which an image is formed by sublimating thermally transferable dyes, and more specifically to the image recording material comprising an image receiving sheet which gives an image having excellent surface glossiness, high acceptability of dyes, stiffness comparative to a silver halide photographic color paper, reduced incompatibility when affixed on a board or reduced curling characteristics without discoloration or smudge, and an ink sheet which is high sensitive and good in color reproduction and contains a dye giving an image having good image stability.
As a color or monochrome image forming technology, the technology has been known in that an ink sheet containing a thermal transferable dye such as a sublimable dye is in contact with an image-receiving layer of a image-receiving element and is heated by a thermal head, etc. so that the sublimable dye described above is transferred imagewise to the image-receiving layer. The image recording method is a digital image recording method which is capable of reproducing image quality parallel to a conventional silver halide photography, and a printer, and an ink sheet and an image receiving sheet have been developed in resent years. However the image formed by the sublimable dye has, despite of good image quality, a problem of poor image storage stability, particularly it is liable to discolor by light or smudge.
A binder composing of the image receiving layer has been studied in order to improve the image storage stability formed by sublimation dye transfer method hitherto. A technology is disclosed in Japanese Patent Open to Public Publication (JP-A) No. 36-319188 that an image receiving material having good image storage ability is obtained by employing a copolymer resin comprising acrylonitrile and styrene as an essential component, which has not brought satisfactory result and has raise a problem of reducing image density.
On one hand, a post chelate dye image formed by reacting a post chelate dye as the sublimable dye with a metal ion containing compound (metal source) improves image storage stability markedly in comparison with the conventional dye image. It is known that the higher the chelating ratio of bonding the chelate dye supplied from the ink sheet to the metal source in the image receiving layer, the more stable the post chelate dye image is. The image receiving sheet formed by the post chelate dye does not produce discloration or smudge and is excellent in stability against light in comparison with the conventional sublimable dye image when it is stored for a long time.
While the image employing the post chelate dye is better than the conventional sublimable material, it has a problem that it is affected by oxygen or moisture in the air sintered into the image receiving layer and the storage stability is deteriorated by that the chelate dye decomposed by oxygen or moisture when it is stored in s severe circumstances for long period.
As the high definition image receiving sheet parallel to the convnetional silver halide photography, those causing no image defects during the image forming, and having excellent surface glossiness of the image receiving layer, high acceptability of dyes, stiffness comparative to a silver halide photographic color paper, and reduced incompatibility when affixed on a board or reduced curling characteristics.
The object of the present invention is to provide a image receiving material which does not cause discoloration or smudge of image and is excellent in glossiness and high accepting ability of dye (i.e., high sensitivity) even though it is stored under severe circumstances such as high temperature and high humidity for ling period.
The thermally transferable recording material and its embodiments of the invention are described.
A thermally transferable recording material to form an image by sublimating a thermally transferable dye, which material comprises an image receiving sheet capable of accepting thermally transferable dye and having a first support and an image receiving layer provided on the first support, wherein the image receiving layer comprises a metal ion containing compound capable of forming chelate with the thermally transferable dye and an acryl resin composed of styrene and acrylonitrile as component unit.
The metal ion containing compound described above is preferably that represented by MX. Here M is a monovalent or poly valent metal belong to Group I through Group VIII of the periodic table, X represents 
wherein Z is an alkyl, aryl, alkoxy, acyl, alkoxycarbonyl, carbamoyl group, a halogen or hydrogen atom; R and Rxe2x80x2 represent an alkyl or aryl group, each of which may be same or different, ring may be formed by boding R with Z or Rxe2x80x2 with Z, with proviso that R and Rxe2x80x2 are not methyl group simultaneously when Z is hydrogen atom.
It is preferred that the acryl resin described above comprises acrylonitrile-styrene resin.
The first support preferably comprises a porous resin layer.
It is preferred that the first support further comprises a paper layer, and that the porous resin layer is provided between the paper layer and the image receiving layer.
It is also preferred that the image receiving sheet comprises a coating layer of aqueous dispersion of resin on an opposite side of the porous resin layer with reference to the paper layer.
The coating layer of aqueous dispersion of resin is preferably a hardenable resin.
The image receiving sheet preferably comprises a back resin layer having higher elastic modulus than tensile elastic modulus of the porous resin layer on an opposite side of the porous resin layer with reference to the paper layer.
It is preferred that the porous resin layer contains polyester.
The polyester is preferable to contain polyethylene-terephthalate.
Tensile elastic modulus of the backing resin layer is preferably more than 1.5 times of that of the porous resin layer.
It is more preferable the tensile elastic modulus of the backing resin layer more than 2.0 times of that of the porous resin layer.
The porous resin layer preferably has specific gravity of 0.5 to 0.9.
It is preferred that the image receiving sheet comprises a back coat layer containing fine particles of inorganic or organic compound and binder on opposite side concerning overlay surface of the porous resin layer.
The back coat layer preferably contain an antistatic agent.
The thermal transfer recording material preferably comprises an ink sheet comprising a second support and an ink layer provided on the second support, and the ink sheet contains the thermally transferable dye.
It is preferable that the thermally transferable dye is that represented by the formula (I) shown below. 
In the formula, R1 and R2 independently represent a substituted or non-substituted alkyl group, R3 represents a substituent. n is an integer of 0 to 4, R3 may be same or different when n is 2 or more. R4 is a straight chain alkyl group having two or more carbon atoms, a cycloalkyl, branched alkyl (excepting tertiary alkyl), aryl, alkoxy, aryloxy or amino group. R5 and R6 independently represent a hydrogen atom or a substituent.
In the Formula I, R4 or R5 is preferably an aryl group having a substituent at ortho position.
In the Formula I, at least one of R4, R5 and R6 is preferably a branched, but not tertiary, alkyl group.